Helicopter tail rotors provide anti-torque forces to maintain stabilized flight and further provide aircraft heading control. With the use of larger helicopter structures, for increased cargo capacity, larger main rotors are utilized resulting in a larger torque on the helicopter airframe. To counter this larger torque, improved tail rotors are required.
Two typical methods of improving the performance of a tail rotor include increasing the rotor blade radius and increasing the number of rotor blades. Increasing the rotor blade radius is undesirable as an increased radius reduces the clearance between the main rotor and tail rotor. Increasing the number of blades in a tail rotor results in an increased tail rotor thrust without increasing the rotor radius. However, multi-bladed tail rotors require a gimbled hub adding extra weight to the tail rotor as well as resulting in a more complex hub than typically used for a two-bladed rotor. Instead of a gimbled hub, a composite hub may be used. A soft-inplane composite hub is very difficult to make stable inplane, and a stiff-inplane hub can be had only by paying a severe weight penalty. Furthermore, rigid four-bladed stiff-inplane tail rotors tend to be heavy because of high loads while articulated and soft-inplane four-bladed tail rotors introduce stability problems into the system.
A need has thus arisen for an improved tail rotor for a helicopter which produces increased tail rotor thrust without an increase in blade radius or tip speed. Such an improved tail rotor must produce increased anti-torque thrust efficiently without adding appreciable weight to the tail rotor of the helicopter.